There are many types of marine instruments available for commercial and pleasure craft today. Some of them include devices for measuring water locating fish. The present invention has particular application for the mounting of fish finding sonar devices, and particularly of the type called a searchlight sonar. A sonar is an echo sounder which includes a transducer to emit a soundbeam downwardly from the boat. When the beam strikes something, such as the bottom or a fish, it will reflect an echo back to the transducer. This is converted to electrical energy, amplified and displayed as information on a screen. It may also display information on a paper graph, flashing devices and even on video displays.
While echo sounders initially were employed to give information about depth, more sophisticated types of devices provide information about the location of fish, both individuals and schools, as well as, to the type of bottom that is located below and around the boat.
A searchlight type of sonar employs a narrow soundbeam that can be pointed in a variety of directions. Generally speaking, the beam is directed in a forward and downward direction. For example, it may be projected downwardly from the boat at 45.degree. while simultaneously the beam is oscillated back and forth over an arc which typically might be 90.degree. or can even approach 180.degree.. It is to this type of mechanism that the present invention has particular applicability.